1. Field of the Invention
The invention is directed to purified and isolated ACPL polypeptides, the nucleic acids encoding such polypeptides, processes for production of recombinant forms of such polypeptides, antibodies generated against these polypeptides, fragmented peptides derived from these polypeptides, the use of such polypeptides and fragmented peptides as molecular weight markers, the use of such polypeptides and fragmented peptides as controls for peptide fragmentation, and kits comprising these reagents. The invention is further directed to the use of ACPL polypeptides, the nucleic acids encoding such polypeptides, and antibodies generated against these polypeptides in the study of cell signaling in response to IL-18 stimulation, and inducible protein expression systems based on the involvement of ACPL polypeptides in cell signaling.
2. Description of Related Art
The IL-1 type I receptor (IL-1R) mediates the biological effects of IL-1. Activities attributed to IL-1α and IL-1β include induction of inflammatory cytokines and other inflammatory responses including prostaglandins, metalloproteinases, adhesion molecules, acute phase proteins, hematopoiesis, fever, bone resorption, and Th2 cell growth and differentiation.
IL-1 has been implicated in chronic inflammatory diseases, such as rheumatoid arthritis and inflammatory bowel disease. There is increasing evidence that IL-1 plays a role in osteoporosis. All of these activities are initiated by the signaling function of the cytoplasmic portion of the type I IL-1R. IL-1ra inhibits the activities of IL-1 by binding to the type I IL-1 receptor, thereby blocking access to IL-1α and IL-1β while eliciting no biological response of its own.
IL-18 is a homolog of IL-1α and IL-1β, and may mediate its activities via a receptor homologous to IL-1R, IL-1 receptor related protein 1 (IL-1RrpI) (See Parnet et al., J. Biol. Chem 271:3967, 1996, and Torigoe et al., J. Biol. Chem 272:25737, 1997). IL-18 acts as a stimulator of Th1 cell growth and differentiation, and is a potent inducer of interferon production from Th1 cells. IL-18 enhances NK cell killing activity and has been implicated in septic shock, liver destruction, and diabetes. Furthermore IL-18 exhibits in vivo antitumor effects in mice, which are immunologically mediated (Micallef et al., Cancer Immunol. Immunother. 43:361, 1997).
The discovery and identification of proteins is at the forefront of modern molecular biology and biochemistry.
The identification of the primary structure, or sequence, of a sample protein is the culmination of an arduous process of experimentation. In order to identify an unknown sample protein, the investigator can rely upon comparison of the unknown sample protein to known peptides using a variety of techniques known to those skilled in the art. For instance, proteins are routinely analyzed using techniques such as electrophoresis, sedimentation, chromatography, and mass spectrometry.
Comparison of an unknown protein sample to polypeptides of known molecular weight allows a determination of the apparent molecular weight of the unknown protein sample (T. D. Brock and M. T. Madigan, Biology of Microorganisms 76-77 (Prentice Hall, 6d ed. 1991)). Protein molecular weight standards are commercially available to assist in the estimation of molecular weights of unknown protein samples (New England Biolabs Inc. Catalog:130-131, 1995; J. L. Hartley, U.S. Pat. No. 5,449,758). However, the molecular weight standards may not correspond closely enough in size to the unknown sample protein to allow an accurate estimation of apparent molecular weight.
The difficulty in estimation of molecular weight is compounded in the case of proteins that are subjected to fragmentation by chemical or enzymatic means (A. L. Lehninger, Biochemistry 106-108 (Worth Books, 2d ed. 1981)). Chemical fragmentation can be achieved by incubation of a protein with a chemical, such as cyanogen bromide, which leads to cleavage of the peptide bond on the carboxyl side of methionine residues (E. Gross, Methods in Enz. 11:238-255, 1967). Enzymatic fragmentation of a protein can be achieved by incubation of a protein with a protease that cleaves at multiple amino acid residues (D. W. Cleveland et al., J. Biol. Chem. 252:1102-1106, 1977). Enzymatic fragmentation of a protein can also be achieved by incubation of a protein with a protease, such as Achromobacter protease I (F. Sakiyama and A. Nakata, U.S. Pat. No. 5,248,599; T. Masaki et al., Biochim. Biophys. Acta 660:44-50, 1981; T. Masaki et al., Biochim. Biophys. Acta 660:51-55, 1981), which leads to cleavage of the peptide bond on the carboxyl side of lysine residues. The molecular weights of the fragmented peptides can cover a large range of molecular weights and the peptides can be numerous. Variations in the degree of fragmentation can also be accomplished (D. W. Cleveland et al., J. Biol. Chem. 252:1102-1106, 1977).
The unique nature of the composition of a protein with regard to its specific amino acid constituents results in a unique positioning of cleavage sites within the protein. Specific fragmentation of a protein by chemical or enzymatic cleavage results in a unique “peptide fingerprint” (D. W. Cleveland et al., J. Biol. Chem. 252:1102-1106, 1977; M. Brown et al., J. Gen. Virol. 50:309-316, 1980). Consequently, cleavage at specific sites results in reproducible fragmentation of a given protein into peptides of precise molecular weights. Furthermore, these peptides possess unique charge characteristics that determine the isoelectric pH of the peptide. These unique characteristics can be exploited using a variety of electrophoretic and other techniques (T. D. Brock and M. T. Madigan, Biology of Microorganisms 76-77 (Prentice Hall, 6d ed. 1991)).
When a peptide fingerprint of an unknown protein is obtained, this can be compared to a database of known proteins to assist in the identification of the unknown protein (W. J. Henzel et al., Proc. Natl. Acad. Sci. USA 90:5011-5015, 1993; B. Thiede et al., Electrophoresis 1996, 17:588-599, 1996). A variety of computer software programs are accessible via the Internet to the skilled artisan for the facilitation of such comparisons, such as MultiIdent, PeptideSearch, and ProFound. These programs allow the user to specify the cleavage agent and the molecular weights of the fragmented peptides within a designated tolerance. The programs compare these molecular weights to protein databases to assist in the elucidation of the identity of the sample protein. Accurate information concerning the number of fragmented peptides and the precise molecular weight of those peptides is required for accurate identification. Therefore, increasing the accuracy in the determination of the number of fragmented peptides and the precise molecular weight of those peptides should result in enhanced success in the identification of unknown proteins.
Fragmentation of proteins is further employed for the production of fragments for amino acid composition analysis and protein sequencing (P. Matsudiara, J. Biol. Chem. 262:10035-10038, 1987; C. Eckerskorn et al., Electrophoresis 1988, 9:830-838, 1988), particularly the production of fragments from proteins with a “blocked” N-terminus. In addition, fragmentation of proteins can be used in the preparation of peptides for mass spectrometry (W. J. Henzel et al., Proc. Natl. Acad. Sci. USA 90:5011-5015, 1993; B. Thiede et al., Electrophoresis 1996, 17:588-599, 1996), for immunization, for affinity selection (R. A. Brown, U.S. Pat. No. 5,151,412), for determination of modification sites (e.g. phosphorylation), for generation of active biological compounds (T. D. Brock and M. T. Madigan, Biology of Microorganisms 300-301 (Prentice Hall, 6d ed. 1991)), and for differentiation of homologous proteins (M. Brown et al., J. Gen. Virol. 50:309-316, 1980).
In view of the continuing interest in protein research and the elucidation of protein structure and properties, there exists a need in the art for polypeptides suitable for use in peptide fragmentation studies and in molecular weight measurements.